This invention relates to a method and apparatus for load balancing in a wireless network. For example, this invention is directed to a technique for balancing bearer load across a bank of traffic processors associated with a high-availability radio network controller (RNC). Instantaneous measures (e.g. processor occupancy) are used as one parameter for such load balancing. Predictive measures are used as another parameter. The predictive measures indicate the degree to which a given processor can become busy in the next few intervals of time and is based on the unrealized potential as derived from the established data rate of bearer sessions. The overall technique described herein allows for an even distribution of highly bursty traffic, with an objective of preserving call quality during periods of increased network congestion.
While the invention is particularly directed to the art of load balancing in wireless networks, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in other applications where analysis of predictive measures of traffic patterns would be advantageous.
By way of background, with reference to FIG. 1, a typical cellular wireless communication system 10 is comprised of a plurality of cells 12, each occupying a separate geographical area in which mobile devices 15 may be roaming. Each cell usually includes a cell site 14 having known hardware necessary for providing wireless communication coverage to a plurality of wireless terminals, such as the mobile devices, or wireless terminals 15 within the cell. Examples of such hardware can include, but is not limited to radio frequency transmitters and receivers, antenna systems, interface equipment and power sources.
Each cell site 14 typically communicates with one or more active processes having application processors, such as those shown at 16, which handle access to system resources such as radios, channels and the like for the cell. Software applications running on these application processors 16 perform the control and traffic processing necessary to establish, maintain and transition wireless voice and data calls. Several cell sites typically communicate with a Radio Network Controller (RNC) 18, which switches wireless calls to a wireless Core Network 20, which in turn switches calls to, as an example, wired central offices to enable mobile terminals to communicate with phones over the Public Switched Telephone Network (PSTN) (not shown).
Radio access network traffic can be either in the form of control messages or traffic packets. Control messages are used to establish calls, manage the radio links associated with call, page user equipment, update the location of user equipment, etc. Traffic packets contain end-user data such as voice, browsed web pages, file transfers, etc.
It is common that processing of control messages is performed on one type of processor, called a control processor (CP), and the processing of traffic packets is performed on a different type of processor, called a traffic processor (TP). Typically, there are far more traffic packets than control messages for most user scenarios. So, there are typically many traffic processors (TPs) for every control processor (CP). As such, there is a hierarchical arrangement of control processors (CPs) to traffic processors (TPs) wherein the control processors (CPs) have the responsibility of distributing new user sessions to subtending traffic processors (TPs) (calls and user sessions are used interchangeably). It is important for a control processor (CP) to distribute the load on its subtending traffic processors (TPs) in a manner that prevents occurrences where some traffic processors (TPs) are in overload, from an occupancy/resource perspective, while other traffic processors (TPs) are relatively idle. In Second-Generation (2G) wireless systems, it has usually been sufficient to distribute user sessions based on instantaneous measures, such as the number of current user sessions in progress or processor occupancy.
Third Generation (3G) wireless systems are characterized by very high data rates (e.g. 2 megabytes per second and higher) and a level of traffic variability that far exceeds that experienced in the traditional voice only and Second Generation (2G) cellular data systems. This leads to rapid ramp-ups and ramp-downs in the traffic demands of a given user and, thus, for the radio access network as a whole.
The actual data rate for a given user session is partially confined to the data rate negotiated with the Radio Network Controller (RNC). Typical data rates could be 32K, 64K, 128K, 384K, 2 MB, etc. Separate data rates are established for uplink (mobile to network) and downlink (network to mobile) directions. It is also typical that the downlink data rate is significantly higher than the uplink data rate. A data rate is negotiated at the time that the session is established; however, that data rate may be dynamically reduced over time by the radio network controller (RNC). Reasons for doing this could be that the user session did not have sufficiently high utilization for a prolonged period of time, or as a means to reduce air interface congestion.
Typically, the load balancing methods, including those described in accordance with the invention below, here are applicable to all forms of traffic data and do not need to distinguish between circuit voice traffic, conversational packet traffic, streaming video, background data, etc.
Such load balancing methods serve to preserve the integrity of user sessions by pushing off traffic processor (TP) overload control until absolutely necessary. Once a traffic processor (TP) is allowed to go into overload, in a well thought out implementation, the focus shifts from preserving the integrity of user sessions to preserving the integrity of the processor and thus the system.
In this regard, once a TP goes into overload, provided that the overload control mechanisms are ideal, the user sessions will experience increased latency and reduced throughput due to retransmissions. Where the overload controls are inadequate, the processor is likely to reset and all user sessions terminated. This results in a negative reputation for the service provider in the eyes of the end-user, and a negative reputation for the infrastructure manufacturer in the eyes of the service provider. Ultimately, this can lead to the end-user changing service providers and the service provider changing infrastructure manufacturer.
The present invention contemplates a new and improved method and system for load balancing in a wireless network that resolves the above-referenced difficulties and others.